This invention relates to internal combustion two cycle engines. More particularly, this invention relates to a metered induction two cycle engine.
Internal combustion two cycle engines generally comprise a compression chamber in which a fuel/air mixture (generally a fuel/oil/air mixture) is partly compressed and transferred into a combustion chamber for further compression and ignition. The two cycle engines have been configured in a variety of ways, in attempts to improve efficiency, power and other features. Examples of these attempts are represented by U.S. Pat. Nos. 2,136,293; 2,522,649; 3,543,735; 3,880,126 and 3,774,581.
A two cycle engine which does not require the mixing of fuel and oil is presented in U.S. Pat. No. 2,136,293 to Gentry. The engine of the '293 patent inducts air for combustion via a piston device and provides a passage for air to the combustion chamber. The induction of air or mixture (i.e., fuel/air) into the passage results in a full downward (i.e., induction) stroke of the piston against full manifold vacuum. The injector piston includes piston porting that requires the whole induction stroke of the piston be made against high vacuum on the piston head followed by a rush of inducted material, thus increasing the pumping losses.
An increased power two cycle engine is presented in U.S. Pat. No. 2,522,649 to Tenney, wherein porting of two pistons (and their relative size) is arranged to provide supercharging of combustion cylinder for high max output. A lack of significant clearance volume above the pumping piston to be re-expanded before drawing new charge through results in high negative pumping work during light load operation. FIG. 11 of U.S. Pat. No. 2,522,649 shows an alternate single-crank-throw variant of the basic disclosure which, coincidentally provides some re-expansion volume to the transport duct except during those portions of the induction stroke when the port is covered by the piston extension. Energy is lost in the power stroke of the combustion piston due to early release of pressure during the cycle. Further, the impingement of hot combustion gases under pressure against the pumping piston as it closes off the transfer duct is expected to result in pumping piston galling and seizure.
A two cycle diesel engine is presented in U.S. Pat. No. 3,543,735 to Kruckenberg et al. The engine includes a pumping cylinder in communication with a power cylinder via a conduit having a significant volume. The pistons are at a 90.degree. relationship with each other. This engine is limited to diesel operation since any attempt to operate it with a throttled inlet would result in gross back-flow all the way from the exhaust manifold back through the combustion cylinder, the conduit and into the pumping cylinder area. This is caused by the air inlet port being uncovered by the piston in the pumping cylinder at about the same time that the inlet ports are covered by the piston in the power cylinder, thus precluding any recompression of the inducted gases before their exposure to exhaust conditions. Furthermore, the use of the pure piston-ported inlets constrains the inlet port opening and closing timing to fixed points in the piston stroke and precludes the use of different quantities of gas induction stroke at various load conditions.
Split cylinder engines are presented in U.S. Pat. No. 3,880,126 to Thurston et al and U.S. Pat. No. 3,774,581 to Lundy, wherein the engine includes an induction cylinder and a power cylinder with a chamber therebetween. A spark plug is disposed in the chamber for ignition of the mixture. Mechanical valves (i.e., poppet valves) are employed to control flow, which will present a severe restriction on engine operation speeds because of the relatively small portion of an engine revolution during which they must be opened and closed for two-cycle operation. No re-expansion volume is provided in open communication with the induction cylinder, which results in the stroke of the piston in the induction cylinder being made entirely against the restraining force of intake manifold vacuum. The transfer vales between the induction and combustion cylinders are subject to combustion temperature and pressure, which will restrict operating speeds, due to the heavy construction required. The engine of U.S. Pat. No. 3,774,581 includes a combination poppet and reed valve at the inlet port of the power cylinder. The reed feature of the valve allows for late opening of the intake valve and prevents development in the induction cylinder of vacuum which is even more impaired than that in the intake manifold.
Generally outboard motors are two cycle engines. These engines generally comprise a piston which moves upward in a cylinder thereby compressing a live charge above the piston prior to its ignition by a spark plug. By this upward piston motion a vacuum is created in a crankcase and a combustible gas flows into this area surrounding the crankshaft and a connecting rod through a reed valve at the crankcase. As the piston descends on its power stroke, the gases in the crankcase are compressed (i.e., the reed valve closes automatically when the crankcase pressure rises above inlet manifold pressure) until such time as the piston uncovers an intake port in the cylinder, thus allowing these compressed gases to rush into a cylinder and expel the burned gases from the last explosion into an exhaust manifold. Oil must be added to the fuel to lubricate the lower portions of the engine, since no reservoir of liquid oil may be maintained in a crankcase that is serving as a transport chamber for induction gases.